The present invention relates, in general, to optical scanning systems and more particularly to an optical system for reading bar codes carried by moving packages such as cartons on a conveyor.
The use of optical bar codes for identifying a wide variety of goods is now well established, and such codes are commonly used for pricing, inventory control and for a variety of record keeping purposes in retail, wholesale and manufacturing operations. Such codes have proliferated with the increased use of automatic data processing systems, and this has produced a strong demand for reliable systems which will rapidly and accurately read the information provided by the codes, transfer that information to a computer, a data storage system, a read-out display, a control device, or the like. Extremely fast and accurate reading of these codes is particularly necessary if the advantages of computer control are to be realized, for although such codes may be read by a variety of available devices, or even by visual inspection, and the information then transferred to suitable data storage or handling equipment, prior art readers fail to take advantage of the high speed and accuracy of modern data processing equipment.
Numerous reading devices such as optical scanning cameras, laser systems and like optical devices, as well as a variety of mechanical systems have been developed for detecting bar codes and for providing corresponding electrical signals. Typical of the prior art systems are those shown and described in U.S. Pat. Nos. 4,135,663 to Nojiri et al., 4,136,821 to Sugiura et al., and 4,140,271 to Nojiri et al. Although such presently available bar code readers are sufficiently accurate to be commercially valuable, many problems are still encountered with them, and none has been found to be entirely satisfactory. For example, many prior devices are incapable of reading bar codes that are printed on background material that provides a poor contrast with the printing ink, where the printing has been done inaccurately or incompletely, where the printing ink has been smudged, or where dirt gets on the code label and provides false readings.
A particular problem is encountered where it is desired to detect codes printed on moving targets such as containers on a conveyor, for the motion of the code label compounds the problems described above. The reading of bar code labels on conveyor-carried containers or packages presents additional difficulties where the container can become mislocated on the conveyor so that the label is out of focus or at an angle with respect to the scanning camera. Thus, the container can be twisted or tilted on the conveyor so that the code markings are foreshortened with respect to the reader, thus making an accurate detection of the code extremely difficult and, with many prior art devices, substantially impossible. Because of such problems, it becomes necessary to limit the maximum speed at which a conveyor can be operated and still provide some assurance of a reasonable degree of reliability in reading the code markings, but such a limitation prevents the user of the equipment from realizing the benefits of high speed computerized data handling systems, and the optical reader becomes the limiting factor in the system. The recent introduction of laser scanners has solved some of these problems, since lasers can be utilized to illuminate and scan bar code labels at high speeds and with improved focus. But even so, even minor anomolies in the printed code on a container or label can cause serious errors in a read-out, and this, taken with the high initial expense and the high maintenance costs of laser devices, have made such systems unsatisfactory.
The various problems encountered in prior art systems as outlined above have been overcome by the present invention, which provides rapid and accurate reading of bar codes at lower cost and with greater reliability than was heretofore possible. The reader of the present invention is capable of providing multiple scans of a bar code as it passes by the reader at a high rate of speed, and the data handling system of the invention is capable of producing an accurate read-out of the coded information with a high degree of resolution and reliability.